The present invention relates to a connecting rod for a reciprocating piston of an internal combustion engine, and more particularly to an improved crankpin bearing for such a connecting rod.
Connecting rods typically have two-piece crankpin bearings for connecting the lower end of the rod to a crankpin of a crankshaft. The two-piece assembly comprises an arcuate-shaped bearing portion integrally formed on the lower end of the rod, and a cap member which is assembled to the bearing portion by means of a pair of cap screws. In the past, these cap screws have typically been identical in size and shape with each screw torqued with substantially identical forces to assemble the cap member on the arcuate-shaped bearing portion around the crankshaft.
Under normal operation, a hydrodynamic oil film is provided between the outer surface of the rotating crankpin of the crankshaft and the inner surface of the crankpin bearing. Thus, friction is minimized resulting in relatively low heat generation. However, when running in a failure mode, for example when an engine runs out oil, there is a loss of lubrication between the crankpin bearing and the crankpin, and heat rapidly builds up in the crankpin bearing. The loss of oil film results in increased friction between the rotating surfaces of the crankpin and crankpin bearing which in turn increases the load on the engine. This increased load also further increases friction. As a result there is an exponential increase in the amount of heat generated between these two rotating surfaces which occurs in a very short period of time. The temperature of the bearing thus increases at an extremely rapid rate, and if the engine is not stopped will reach the yield temperature of the components of the crankpin bearing resulting in self-destruction of the bearing and massive damage to the interior of the engine. It is therefore desirable to provide some mechanism for stopping the engine when running in a failure mode of operation so that the temperature of the crankpin bearing never reaches the yield temperature of its components.